Range finders are very popular devices for determining a proximate range or distance of a target object. One type is a camera-based range finder, which projects a field of spots onto the target object and captures an image of the spots with a remote camera. The range finder uses the parallax shift of the spots in the captured image to determine the object's range. The greater the parallax shift, the closer the object. However, the image resolution of the spots can be very poor for far objects, such that the range finder is limited to use with near objects.
Another type is an intensity-based range finder, which blasts full visible light toward the target object and captures the light the object reflects back. The range finder uses the intensity of the reflected light to determine the object's range. The dimmer the intensity, the farther the object. However, different colors can reflect different intensities, such that different-colored objects at the same range can reflect different light intensities. Similarly, if the range finder has dirt, smudges, or other particles on it, these particles can block some of the reflected light, thereby dimming the intensity of the reflected light to make the object appear farther away than it is. Or these particles can themselves reflect back light emitted by the range finder, thereby brightening the intensity of the reflected light to make the object appear closer than it is. Also, this range finder is generally limited to use with very close objects, e.g., on the order of millimeters.
A third type is a time-of-flight range finder, which emits a light pulse and detects a pulse reflected back from the target object. The range finder uses the phase shift between the emitted and reflected pulses and the speed of light to determine the time lapse between the pulses. The greater the time lapse, the farther the object. However, there are several issues with this range finder. It can be power inefficient. The emission wavelengths can interfere with the retina of the human eye, raising eye safety concerns. And the resolution can be low to moderate, making object detection less accurate.
Accordingly, currently available range finders often do not provide the desirable accuracy and performance that many applications require.